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Stockholders' Equity - Additional Information (Detail) (USD $)
In Millions, except Share data, unless otherwise specified |
3 Months Ended | 6 Months Ended | 3 Months Ended | 6 Months Ended | 3 Months Ended | 6 Months Ended | 3 Months Ended | 6 Months Ended | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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Jun. 30, 2013
|
Jun. 30, 2013
|
Jun. 30, 2013
Warrants [Member]
|
Jun. 30, 2013
August 2008 offering [Member]
|
Dec. 31, 2012
August 2008 offering [Member]
|
Jun. 30, 2013
August 2008 offering [Member]
Warrants [Member]
|
Jun. 30, 2013
August 2008 offering [Member]
Warrants [Member]
|
Jun. 30, 2013
Cashless exercise of warrants [Member]
Warrants [Member]
|
Jun. 30, 2013
October 2009 offering [Member]
|
Dec. 31, 2012
October 2009 offering [Member]
|
Jun. 30, 2013
October 2009 offering [Member]
Warrants [Member]
|
Jun. 30, 2013
October 2009 offering [Member]
Warrants [Member]
|
Jun. 30, 2013
March 2011 offering [Member]
|
Dec. 31, 2012
March 2011 offering [Member]
|
Jun. 30, 2013
March 2011 offering [Member]
Warrants [Member]
|
Jun. 30, 2013
March 2011 offering [Member]
Warrants [Member]
|
|
| Class of Warrant or Right [Line Items] | ||||||||||||||||
| Warrants exercised | 231,711 | 1,716,941 | ||||||||||||||
| Net proceeds from warrants exercises | $ 0.6 | |||||||||||||||
| Common stock shares issued for cashless conversion of warrants | 1,153,179 | |||||||||||||||
| Reclassification of fair value from liability to permanent equity of warrants exercised | 7.5 | 7.5 | ||||||||||||||
| Warrants outstanding | 9,600,000 | 9,600,000 | 1,312,459 | 3,058,811 | 4,287,940 | 4,287,940 | 4,033,783 | 4,236,083 | ||||||||
| Change in fair value of common stock warrants | $ 2.7 | $ 3.1 | $ 0.8 | $ 2.2 | $ 2.3 | $ 3.6 | ||||||||||